Although there have been attempts to deposit metal oxides, such as TiO2 and SrTiO3, during semiconductor fabrication, thermal oxidation of metals in the fabrication of capacitors has been limited since an initial oxide layer prohibits further diffusion during thermal oxidation. As a result the use of high dielectric constant oxidized metals has been limited in semiconductor capacitor fabrication. One such metal, titanium dioxide, has a dielectric constant 2-15 times greater than present semiconductor capacitor dielectrics such as silicon nitride, while titanates are 2-1000 times greater.
In the January 1996 issue of Material Research, Vol. 11, No. 1, an article entitled ELECTROCHEMICAL SYNTHESIS OF BARIUM TITANATE THIN FILMS, R. R. Bacsa et al. describes the synthesizing of polycrystalline films of barium titanate on titanium substrates by the galvanostatic anodization of titanium to form a material which has a dielectric constant of 200.
The invention includes new capacitor structures and dielectrics and methods for forming such capacitors and dielectrics.
In one exemplary embodiment the capacitor of the invention is formed by a process using only two deposition steps. The capacitor has first and second conductive plates and a dielectric is formed from the first conductive plate.
In one exemplary process in accordance with the present invention a metal layer is deposited and at least partially oxidized in an electrolytic solution. The metal oxide formed during this oxidation forms the dielectric of the capacitor. Portions not oxidized may form at least a portion of a capacitor plate.
In one exemplary implementation in accordance with the present invention, a metal layer is deposited to overlie a first capacitor plate fabricated on a semiconductor wafer. The wafer is placed in an electrolyte conducive to forming an oxide with the metal. A potential is applied across the electrolyte and the metal, and at least a portion of the metal oxidizes. In a preferred embodiment the metal is titanium and titanium dioxide is formed during the electrochemical reaction. The capacitor fabrication is completed with the formation of a second capacitor plate overlying the oxidized metal layer. The oxidized metal layer functions as the dielectric of the capacitor and has a high dielectric constant.